This invention relates to turbocharger control systems.
It is known that increasing the pressure of the air supplied to an internal combustion engine will increase the horsepower output, and various types of supercharging and turbocharging arrangements have previously been proposed for internal combustion engines.
However, there are a number of factors which go into the optimum operation of a turbocharger or a supercharger. Thus, for example, when a turbocharger is operated by the hot exhaust gases from an engine, the back pressure on the engine is increased, and the efficiency of the engine is thereby reduced somewhat as a result of this increased back pressure. In addition, the compressor of a turbocharger must not be overdriven. More specifically, above a certain rate of rotation, with the diffuser vanes in a predetermined orientation or configuration, the compressor will reach an undesired condition in which cavitation, or "surge" may occur, if the compressor speed is not in keeping with the appropriate mass flow rate for that given compressor speed and configuration or geometry. Under these conditions the compressor may suffer mechanical damage. This undesired phenomenon occurs at a driving speed which is only slightly above the optimum operating point of the compressor. Up to the present time, although superchargers and turbochargers have been employed, they have generally not been operated at the optimum operating points for highest overall engine efficiency; but instead, the superchargers have generally either been operated at a relatively low efficiency region where only a portion of the potential increase in horsepower has been realized, or at such a high level that intermittent cavitation or other failure of the supercharger to supply additional air to the intake manifold occurs. In other prior systems, using what is known as "waste-gate controls" a significant portion of the engine exhaust gases have been selectively diverted to the atmosphere to control the turbocharger rotational speed. Such controls waste a portion of the available energy which could otherwise be utilized for useful purposes. Accordingly, the very significant potential of turbochargers, which can increase engine power by in the order of sixty (60%) percent when optimally employed, has generally not been realized.
A principal object of the present invention is therefore, to provide a control system for the operation of a turbocharger whereby the diesel engine and turbocharger combination is efficiently operated at close to the maximum power output capability throughout the full power operating range of the engine, but safely below the "cavitation" or "stall" region of the compressor, whereby reliable high efficiency and high power operation is achieved. A subordinate object of the present invention is to accomplish the foregoing with a simple and reliable electronic circuit implementation.